Method and apparatus for continuous underwater mining using plural ships

ABSTRACT

Continuous extraction of solid products from the bottom of the sea by means of at least one endless dredging line provided with buckets. The endless line is lowered to the sea bed from a first ship, the buckets are caused to dredge the surface of the sea bed and the line is then raised to a second ship traveling along a generally parallel course to the first ship after the dredging operation is completed. The line is returned to the first ship along a return path which is at least partially submerged.

United States Patent 1191 Gauthier et al.

[ 1 June 17, 1975 METHOD AND APPARATUS FOR CONTINUOUS UNDERWATER MINING USING PLURAL SHIPS [75] Inventors: Michel Gauthier, Renan; Marcel Tessier; Daniel F leruy; Michel Jegousse, all of Nantes, France [731 Assignees: Centre National pour IExploitation des Oceans; Le Nickel, both of Paris, France; part interest to each [22] Filed: May 15, 1973 [21] Appl. No.: 360,594

[30] Foreign Application Priority Data May 25, 1972 France 72.18636 [52] U.S. C1. 37/69; 37/195; 43/45; 43/65; 214/13 [51] Int. Cl E02f 5/00 [58] Field of Search 43/45, 6.5, 9, 13, 14; 37/55, 60, 69, 195-, 214/13 [56] References Cited UNITED STATES PATENTS 775,686 11/1904 Smith 37/69 X 983,301 2/1911 Murdock 214/13 2,832,168 4/1958 Brown 43/65 x 3,672,079 6/1972 Masuda Ctal.

3,675,348 7/1972 Dane, Jr. 37/69 FOREIGN PATENTS OR APPLICATIONS 600,067 6/1960 Canada 43/9 1,239,178 7/1971 United Kingdom 37/69 Primary Examiner-Clifford D. Crowder V Attorney, Agent, or Firm-Fleit & Jacobson [5 7 ABSTRACT Continuous extraction of solid products from the bottom of the sea by means of at least one endless dredging line provided with buckets. The endless line is low ered to the sea bed from a first ship, the buckets are caused to dredge the surface of the sea bed and the line is then raised to a second ship traveling along a generally parallel course to the first ship after the dredging operation is completed. The line is returned to the first ship along a return path which is at least partially submerged.

8 Claims, 2 Drawing Figures PATENTEDJIJN 17 1915 F: 8 89 L403 V HUI 3 )DW) )D METHOD AND APPARATUS FOR CONTINUOUS UNDERWATER MINING USING PLURAL SHIPS This invention relates to a method of and an apparatus for continuously extracting solid products which lie on an underwater floor (hereinafter. referred to as the sea bed). The invention is particularly applicable to the continuous extraction, by dredging or harvesting, of deep sea polymetallic modules which, as is known, are of great interest in the recovery of the various metallic values that they contain.

Such polymetallic nodules generally lie at very great depths, of the order of 3000 to 6000 metres, and it is difficult to recover them economically using conventional dredgers. On the other hand, apparatus has already been proposed for effecting such dredging, for example in British Pat. No. 1,239,178. This apparatus comprises an endless line provided at regular intervals with buckets, the line extending downwards towards the sea bed from the bow of a ship and upwards again to the stern of the same ship. In this arrangement the ship has to move laterally or crabwise, to make the sweep of the sea bed as wide as possible. The lateral movement is achieved by means of auxiliary propellers which are mounted along the sides of the ship.

This known system suffers from a number of drawbacks, among which might be mentioned the small quantity of sedimentary material raised by the buckets. Further, it is difficult to control dredging depth for a given length of the endless line. Furthermore, this system necessitates lateral movement of the ship which is a difficult navigational operation.

One of the objects of the present invention, therefore, is to provide a method of the afore-described kind which enables efficient dredging to be carried out whatever the depth of the sea bed to be dredged. Another object of the invention is to provide a method which involves little or no navigational difficulty. A further object of the invention is to provide a method of the above kind which allows simple and efficient control of the dredging parameters. Yet a further object of the invention is to provide a simple apparatus which is relatively easy to operate in performing the method of the invention.

According to the present invention there is provided a method for the continuous extraction of solid products, especially polymetallic nodules, which lie on the sea bed, by means of at least one endless dredging line provided with buckets, characterized in that said endless line is fed down to the sea bed from a first ship or other vessel and is passed upwardly to a second ship or other vessel after dredging the surface of the sea bed, and is returned to the first ship along a return path which is at least partially submerged, and in that the two ships travel along generally parallel courses.

Further according to the present invention there is provided an apparatus for the continuous extraction of solid products, especially polymetallic nodules, which lie on the sea bed, comprising at least two ships, at least one dredging line equipped with buckets, means for lowering said line from one of said ships to the sea bed,-

means for raising said line from the sea bed to the other i of said ships, and means for passing said line to said one ship through a return path which is at least partially submerged.

Use can also be made of a plurality of endless lines fitted with buckets. For instance two lines may each be lowered towards the sea bed from separate laying ships and, after the dredging has been completed, both lines are raised towards the same extractor ship where the buckets can be emptied of nodules. It would also be possible to provide three or more dredging lines and three or more ships, each ship acting as a laying ship for one line and an extractor ship for another line.

It will be readily understood that the method according to the invention enables the dredging depth and/or the length of dredging line resting on the underwater bed to be controlled in an extremely simple manner. This control is obtained by varying the curvature in the partially submerged return path, and it is not necessary to move the ships relatively to each other to effect such variation. Conversely, if it is required to alter the positions of the two ships, for example for reasons of navigation, without changing the dredging parameters, it likewise suffices to vary the curvature in the return portion of the line.

It is also noted that the method according to the invention raises few navigational problems. In fact, it is a simple matter to move the two ships parallel to each other, using what is sometimes known as yoked oxen navigation, one of the ships being the mother ship and the other navigating by reference to the first. Furthermore, the return portion of the line is not an obstacle for other ships, as it is submerged.

Additionally, it is advantageous to deposit the buckets on the sea bed in readiness for operation, before starting their dredging action; this results particularly in greater operational flexibility, in stabilizing the dredging line, and in reducing ineffective skidding of the line of buckets over the sea bed.

The apparatus defined above preferably also comprises means for controlling the curvature in said return position.

Preferably, the means for lowering the dredging line to the sea bed and the means for raising the line comprise winches controlled by the mechanical tension in said return portion.

The apparatus may comprise two ships and a single dredging line. Alternatively, the apparatus may comprise three ships and two dredging lines. The two lines are raised from the sea bed after having dredged, and are brought aboard a common extractor ship to be passed back one to each of two laying ships which are located one on each side of the common extractor ship. Apart from this arrangement enabling the extraction capacity to be doubled by the addition of one ship, it offers the advantage of symmetry of the two dredging lines in relation to the extractor ship, and this facilitates the navigation of the latter ship.

Embodiments of the invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIG. 1 is a diagrammatic pictorial view illustrating one method of carrying out the invention; and,

FIG. 2 is a diagrammatic plan view illustrating another method of carrying out the invention.

The apparatus illustrated in FIG. 1 comprises a laying ship 1, an extractor ship 2, and an endless dredging line 3 fitted with buckets (not shown). The line passes over the two ships and over the sea bed surface F that is to be dredged.

The two ships 1 and 2 move at a speed V, for example, parallel to each other in yoked oxen formation, and into the prevailing wind and current. The two ships are, however, free to shift off their courses in order to make better use of the thrust from their propellers. The distance between the ships may be of the order of 800 metres whereas the depth below water level of the surface to be dredged is of the order of 6000 metres.

It will be appreciated that the speed of travel of a point along the line 3, at a given moment, is composed of two components, viz., the speed at which the line is being fed, and the displacement speed resulting from the movement of the ships.

The endless line 3 fitted with buckets and used for dredging the surface F may comprise a cable, a chain, a rope, a length of strip material which may be jointed, or a combination of such elements. It is made up of various sections or portions which will now be described in more detail.

The laying ship 1 pays out the line which forms a descending portion 4, the direction of movement of which is indicated by the arrow 5; the buckets of this descending portion 4 are, of course, empty. The next portion 6 of theline rests on the sea bed surface F, and preferably carries a row of buckets ready for filling. This arrangement enables:

a. changes in speed of the laying ship 1 to be accommodated without disturbance;

b. the line to be stopped, for example while a bucket is being replaced;

c. the movements of the ascending portion and the descending portion to be independent of each other, so that very considerable operational flexibility is achieved;

d. the dredging loop to be stabilized by preventing it from undergoing vertical movement, with the result that a more precisely defined zone is dredged; and,

e. skidding of the line over the sea bed surface to be reduced, since the buckets that are waiting to be filled act as a brake against skidding of the dredging portion.

The line 3 continues through dredging portion proper 7 which dredges the sea bed surface F over an area 8 of great width, and the length of this area is, of course, equal to the distance over which the ships 1 and 2 move. It will be appreciated that the dredging portion 7 of the line is simultaneously pulledv transversely and forwardly in relation to the portion 6 carrying the waiting buckets. The number of buckets actually involved in dredging the underwater surface will depend mainly upon the lateral distance between the ships 1 and 2, and the overall load on the ascending portion 9 of the line. It'is thus possible to control the number of such buckets and so vary the extraction rate.

It will also be appreciated that the dredging portion 7 is curved at all times, and this results in the following advantages:

i. a reduction of the risk of all the buckets becoming anchored in the sea bed at the same time;

ii. a reduction of the risk of simultaneous skidding of the dredging buckets;

iii. the buckets are brought gradually into motion;

and,

iv. it becomes possible to combine the speed of the,

vessel and the paying-out speed 5 of the line 3, to

obtain a predetermined dredging speed on the sea bed surface. When the buckets have been filled, they are raised along the ascending portion 9 at a speed represented by After the line 3 has passed to the extractor ship 2 i where the buckets are emptied of their sediment load, the line moves back to the laying ship 1 and a partially submerged return portion 11 is formed therein, th movement of which is indicated by arrow 12.

The return line portion 11 enables the two ships to move relatively to each other, and this permits the geometry of the line and the dredging parameters to be controlled, particularly as regards the dredging loop proper. It also enables the same length of line to be used for different dredging depths by varying the curvature of the line.

It is also possible to use the return portion 11 for transferring dredged material to the laying ship 1.

By submerging the loop 11 more deeply, it is also possible to withdraw the dredging portion 7 from the surface F without the necessity of storing the line 3 on the ships 1 and 2.

As stated previously, it is advantageous to employ the tension in the loop 11 to control the winches used for lowering the line 3 from the ship 1 and for raising the line and bringing it aboard the ship 2.

It will be readily appreciated that, when it is required to dredge an area containing polymetallic nodules or other sediments, it is possible to make several sweeps along strips of sea bed surface which have a width of one hundred to several hundred metres and which extend in the most favourable direction as regards navigation.

In the embodiment illustrated in FIG. 2, the elements identical to or performing the same function as those shown in FIG. 1 are designated by like reference numerals. In the embodiment of FIG. 2, use is made of two lines 3a and 3b which dredge two parralel strips 8a and 8b of the sea bed surface. The line 3a is laid from a laying ship 1a and, after having performed the dredging operation, the line is raised and brought aboard an extractor ship 2 and is then passed to the laying ship la by way of a return portion. The line 3b is lowered from a second laying ship 1b and, after having performed its dredging operation, is raised and brought aboard the same extractor vessel 2 as is the line 3a. The line 3b is then passed to its laying vessel 1b,.in the direction indicated by the arrow in this drawing.

The embodiment shown in FIG. 2 enables the quantity of sediment extracted to be doubled by the use of only one additional ship and, as mentioned above, facilitates navigation of the extractor ship 2. The number of lines could of course be further increased by applying the same principles.

What we claim is:

l. A method for the continuous extraction of solid products from a sea bed using at least one endless dredging line having buckets attached thereto, comprising lowering said endless line down to the sea bed from a first ship, causing said buckets to dredge the surface of said sea bed, raising said line upwardly to a second ship traveling along a generally parallel course to said first ship after dredging the surface of said sea bed, returning said line from said second ship to said first ship along a return path which is at least partially submerged and varying the curvature of said line returning to said first ship to control a dredging parameter.

2. The method of claim 1 in which said curvature of said line returning to said first ship is varied as a function of the dredging depth and to control the length of the dredging portion of said line which lies on the surface of said sea bed.

3. The method of claim 1 in which said curvature of said line returning to said first ship is varied as a function of the relative position of said first and second ships to avoid changing the area of the surface of said sea bed being dredged.

4. The method of claim 1 including the step of causing said buckets to lie on the surface of said sea bed in a ready position before commencing the dredging operations.

5. The method of claim 1 including the step of using a second endless dredging line, lowering said second endless dredging line down to said sea bed from a third ship, raising said second line to said second ship and returning said second line to said third ship along a return path which is at least partially submerged, and causing said third ship to travel along a generally parallel course with respect to said first and second ships.

6. An apparatus for the continuous extraction of solid products from a sea bed, comprising at least two ships,

at least one endless dredging line having buckets at tached thereto, means for lowering said line from one of said ships down to the sea bed for dredging the surface of said sea bed, means for raising said line upwardly from the sea bed to the other of said ships after the dredging of the surface of said sea bed, means for returning said line to said one ship along a return path which is at least partially submerged, and means for controlling the curvature of said line along said return path to control a dredging parameter, said ships being adapted to travel along generally parallel courses during said continuous extraction.

7. The apparatus of claim 6 in which said apparatus comprises two ships and a single dredging line.

8. The apparatus of claim 6 in which said apparatus comprises three ships and two dredging lines, one of said ships having means for raising both of said dredging lines at the same time, the two other of said ships being located one on each side of said first ship and each having means for lowering one of said lines toward the surface of said sea bed. 

1. A method for the continuous extraction of solid products from a sea bed using at least one endless dredging line having buckets attached thereto, comprising lowering said endless line down to the sea bed from a first ship, causing said buckets to dredge the surface of said sea bed, raising said line upwardly to a second ship traveling along a generally parallel course to said first ship after dredging the surface of said sea bed, returning said line from said second ship to said first ship along a return path which is at least partially submerged and varying the curvature of said line returning to said first ship to control a dredging parameter.
 2. The method of claim 1 in which said curvature of said line returning to said first ship is varied as a function of the dredging depth and to control the length of the dredging portion of said line which lies on the surface of said sea bed.
 3. The method of claim 1 in which said curvature of said line returning to said first ship is varied as a function of the relative position of said first and second ships to avoid changing the area of the surface of said sea bed being dredged.
 4. The method of claim 1 including the step of causing said buckets to lie on the surface of said sea bed in a ready position before commencing the dredging operations.
 5. The method of claim 1 including the step of using a second endless dredging line, lowering said second endless dredging line down to said sea bed from a third ship, raising said second line to said second ship and returning said second line to said third ship along a return path which is at least partially submerged, and causing said third ship to travel along a generally parallel course with respect to said first and second ships.
 6. An apparatus for the continuous extraction of solid products from a sea bed, comprising at least two ships, at least onE endless dredging line having buckets attached thereto, means for lowering said line from one of said ships down to the sea bed for dredging the surface of said sea bed, means for raising said line upwardly from the sea bed to the other of said ships after the dredging of the surface of said sea bed, means for returning said line to said one ship along a return path which is at least partially submerged, and means for controlling the curvature of said line along said return path to control a dredging parameter, said ships being adapted to travel along generally parallel courses during said continuous extraction.
 7. The apparatus of claim 6 in which said apparatus comprises two ships and a single dredging line.
 8. The apparatus of claim 6 in which said apparatus comprises three ships and two dredging lines, one of said ships having means for raising both of said dredging lines at the same time, the two other of said ships being located one on each side of said first ship and each having means for lowering one of said lines toward the surface of said sea bed. 